This invention relates generally to filters for liquids, and more particularly, to gravity filters which employ filter beds comprising particulate filter media.
Generally, high rate gravity filters, i.e., filters designed to work at high flux rates ranging from 8 to 60 gallons per minute per square foot, include a filter bed composed of particulate filter media. The filter bed is typically supported by planar members which extend over the horizontal cross-section of the filter tank. In such systems the filter liquid is introduced into the tank above the filter bed and flows downwardly through the filter bed, through tubular extensions or the like provided in the supporting member into a chamber below the filter bed. Upon entering this lower tank chamber, the effluent filter liquid exits through an outlet provided in the lower tank chamber.
In the past, the filter bed supporting member included a flat plate which, when used in larger size filter cells, required, in addition to peripheral support flanges provided on the tank wall surfaces, a relatively bulky assembly of beams and support columns extending between the underside of the support plate and the bottom of the tank. Each support structure is quite heavy and has been a costly and time-consuming item in the manufacture of such liquid filters.
Further, such filters are usually cleaned by passing a fluid, such as water or a mixture of air and water, through the bed in a direction opposite to that used during normal filter operations. In such reverse-flow backwashing of filter beds, it is desirable to design the apparatus so that the backwash fluids (liquid and air) are evenly distributed over a horizontal cross-section of the filter bed. In an attempt to attain this goal with respect to the backwash air, a multiplicity of pipes (hereinafter referred to as secondary pipes) of varying length have been provided extending horizontally from a supply header in the lower tank chamber which uniformly distribute the air over the area of the filter bed support plate. Tubular extensions, mounted within the filter bed support plate over its entire area, distribute the backwash air delivered by the secondary pipes in a uniform manner to the filter bed through air passages found therein. However, such filters have proven to be costly since a great many of such secondary pipes are required to achieve sufficient backwash air distribution.
An additional problem encountered in the use and construction of high rate gravity filters is that at least four valves are usually required in order to control the flow of the filter and backwash liquids, namely, a first valve to control the flow of the influent, raw liquid to be filtered, a second valve to control the flow of the effluent filtered liquid, a third valve to control the flow of the influent backwash liquid and a fourth valve to control the flow of the effluent, used backwash liquid. These valves are quite expensive since they are usually equipped with mechanical, automatic command controls that require the use of delicate instrumentation and thereby raise the total cost of constructing and maintaining such filters.
Accordingly, one object of this invention is to provide a new and improved gravity liquid filter.
Another object of the present invention is to provide a new and improved filter support plate for use in gravity liquid filters which is self-supporting.
Still another object of the instant invention is to provide a new and improved apparatus for mounting a filter support plate within a liquid filter.
A further object of this invention is the provision of a new and improved filter support plate which facilitates the distribution of backwash air evenly over the filter bed.
A still further object of the instant invention is to provide a filter support plate which enables the elimination of secondary air distribution tubular extension pipes in the lower filter tank chamber.
One other object of this invention is the provision of a filter apparatus having a reduced number of required valves for controlling the flow of influent and effluent liquids.
Briefly, in accordance with one embodiment of this invention, these and other objects are attained by providing the filter bed support element in the form of a corrugated plate having alternate channels and ridges formed therein. When used for relatively small size filter cells, such plate may be self-supporting, i.e., needs no support other than at points along its periphery. Even when used for relatively large size filter cells, the corrugated plate needs only a single cross or beam support. Another feature of this invention is that in such a case, a header which normally functions as backwash air inlet, may be utilized as the cross support. Channels formed in the corrugated plate serve to uniformly distribute the backwash air delivered by the header to tubular extensions mounted in the plate for delivery to the filter bed.
In another embodiment, the header supports a plurality of crosswise extending channel beams which, in turn, support a planar filter bed support member. The crosswise beams produce the same air distribution effect as channels formed in the corrugated plate.
Yet another feature of the present invention is the provision of an influent filter liquid inlet assembly including a normally open passage for the influent raw liquid and apparatus adapted to automatically close the passage during reverse-flow backwashing of the filter bed upon the backwash fluid reaching a predetermined level in the upper tank chamber, such apparatus being actuated solely by the presence of the backwash fluid. The effluent backwash liquid outlet is located at a higher level within the upper chamber than is this influent filter liquid passage thereby disposing of the need for the previously required valves which controlled the outlet of the effluent backwash water and inlet of the raw liquid to be filtered.